Continuous digesting of cellulosic fibrous material at decreasing pressure with mechanical defibering therebetween



March 1966 VILLAVICENCIO ETAL E. J. 3,238,088 CONTINUOUS DIGESTINGOF GELLULOSIC FIBROUS MATERIAL AT DECREASING PRESSURE WITH MECHANICAL DEFIBERING THEREBETWEEN 2 Sheets-Sheet 1 Filed Dec. 4, 1962 March 1, 1966 E. J. VILLAVICEN CIQ ETAL 3,233,083 CONTINUOUS DIGESTING OF UELLULOSIG FIBROUS MATERIAL AT DECREASING PRESSURE WITH MECHANICAL DEFIBERING THEREBETWEEN 2 Sheets-Sheet 2 Filed Dec. 4,, 1962 INVENTORS foe/A200 J wanw a/clo, Mae/o 5/5444 20.145,

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c A rick/v5 vs United States Patent CONTINUOUS DIGESTING 0F CELLULOSIC Fl- BROUS MATERIAL AT DECREASING PRESSURE WITH MECHANICAL DEFIBERING THEREBE- TWEEN Eduardo J. Villaviceucio, Mario Sierra Rojas, and Salvador Escobar, Mexico City, Mexico, assignors to Cia Industrial de Ayotla, S.A., Mexico City, Mexico Filed Dec. 4, 1962, Ser. No. 242,183

5 Claims. (Cl. 162-19) This invention relates generally to the production of pulp from cellulosic material and more particularly to processes for obtaining paper pulp from bagasse.

Sugar cane bagasse is the residue of the cane remaining after the sugar containing juices have been extracted. This extraction is accomplished by feeding the bagasse into crushing rollers and then through extraction rollers so that the bagasse as it leaves the final expressing mill comprises broken particles of relatively low residuary moisture containing a mixture of pith cells and fiber and only a relatively few percent of the original sugar. It has been recognized that bagasse has an excellent potential as a source for cellulosic fibers for preparing pulp for making various grades of paper and paperboard.

.However, there has been little commercial use of bagasse for this purpose because of problems encountered in refining bagasse into a suitable pulp by any of the usual paper making processes. Bagasse contains a large amount of pith and lignin which must be separated from the desirable fibers in order to produce a finished product of the required strength, flexibility and color. It has been found that when the bagasse is treated with pulp processing chemicals for extracting the undesirable portions from the fiber in the usual concentrations and at the usual temperatures and pressures employed for wood pulp, the bagasse fibers become damaged by loss of some of their mechanical strength and tendto darken from the exposure to high temperature. On the other hand, efforts to process bagasse using a lower concentration of chemicals and lower temperatures have required a process time so long as to be economically unfeasible and results in a product of varying quality.

It is therefore a principal object of this invention to provide a novel process for the continuous production of high grade pulp from bagasse in which the bagasse is given an initial softening and chemical impregnation step in a saturated steam zone at elevated temperatures and pressures, followed by a mechanical defibration at the same temperature and pressure followed in turn by continued exposure at elevated temperatures and pressures to complete the refining and cooking of the pulp.

It is another object of this invention to provide a novel process for the continuous production of high grade pulp from bagasse as set forth in the preceding object in which following the final cooking, the pulp is passed through an additional mechanical defibrating step in which the temperature and pressure are lowered in the defibrator.

It is another object of this invention to provide a novel process for the continuous production of high grade pulp from bagasse which may be carried out using saturated steam in a pressure chamber at lower temperatures and pressures than has heretofore been possible.

It is another object of this invention to provide a novel process for the continuous production of high grade pulp from bagasse which allows the production of a high grade of pulp with a reduced amount of chemicals for separating the lignin and other non-cellulosic materials from the fiber.

It is another object of this invention to provide a novel process for the continuous production of high grade pulp "ice from bagasse which is adaptable to a wide variety of chemical processes in combination with the mechanical processing action.

Still another object of this invention is to provide a novel process for the continuous production of high grade pulp from bagasse which gives an improved and high quality pulp at a minimum cost and requiring a minimum amount of chemicals and processing time.

Further objects and advantages of this invention will readily become apparent to those skilled in the art upon a more complete understanding of the invention as described in the following detailed description of the preferred embodiment of the invention and the apparatus for carrying out the process as shown in the drawings in which:

FIGURE 1 is a side elevational view of the apparatus employed with the process of this invention; and

FIGURE 2 is an enlarged elevational view similar to FIGURE 1 with parts broken away to show the internal construction of the apparatus.

In the apparatus of FIGURES 1 and 2, the bagasse fiber is delivered to an inlet 10 and from there fed by means of a screw 11 into a pressure feed 12. The screw 11 may be driven in any convenient manner such as by the gear box 13 and motor 14. The pressure feed 12 has a feed screw 16 which extends into a tapered conical sect-ion 17 and is driven by a gearbox 18 and motor 19. The tapered conical section 17 is joined by a plug section 22 to one side of a receiving chamber 24. The receiving chamber 24 is also provided with a blow back control indicated generally at 25 together with a steam inlet pipe 26 and a chemical inlet pipe 27 through which the necessary chemicals are added to the pulp during processing. The pressure feed 12 and the plug section 22 serve to close off the opening of chamber 24 by means of a plug formed by the fiber being fed so as to maintain the necessary pressures and temperatures within the reaction Zone, While allowing additional bagasse to 'be fed at a continuous and controlled rate.

From the receiving chamber 24, the bagasse passes into one end of an elongated cylindrical impregnating chamber 30 within which is a screw conveyor 31 which may be rotated through a drive gear indicated at 32. The screw conveyor 31 serves to slowly and uniformly convey the material from the receiving chamber 24 to the outlet 34 while providing sufficient agitation to allow a thorough exposure of the bagasse to the steam and chemicals within the impregnating chamber. By controlling the rate of rotation of the screw conveyor 31, the length of time in which the fiber remains in the impregnating chamber 30 may be controlled as desired. The outlet 34 from the impregnating chamber 30 is connected to a disc refiner or defibrator 36 which may be any of the usual types well known in the art employing rotating discs which abrade and rub the fiber bundles to break them apart and separate them into smaller pieces so that they may be acted upon more efficiently during subsequent treatment.

The disc defibrator 36 has an outlet pipe 37 which is connected through a valve 38 to the inlet 41 of the digesting chamber 40. The digesting chamber 40 is similar in construction to the impregnating chamber 30 and is provided with a screw conveyor 43 also driven by suitable means by drive gear 44. The rotation of the screw conveyor 43 in the digesting chamber 40 may be controlled independently of the rate of speed of the screw conveyor 31 in the impregnating chamber 30, so that the period of time in which the fiber remains in each of these chambers is independently variable.

At the end opposite inlet 41, the digesting chamber 40 has an outlet 46 to discharge the treated fiber pulp into a second disc refiner 48 to give further treatment to the fiber and finish the pulping action. From the second disc refiner 48, the finished pulp is discharged through an outlet 50 which is provided with a pipe 52 for injecting water into the pulp to prevent vaporization of the steam contained therein. This construction requires no blow chamber for receiving the discharged pulp from the digesting chamber 40, since a pressure drop takes place in the disc refiner 48 and the water added through pipe 52 serves to cool the pulp and prevent any flashing as the pulp is discharged at atmospheric pressure.

The bagasse used in this process may be either the whole bagasse as it is discharged from the sugar expressing mills, or it may be cleaned and refined to reduce the pith content. It is recognized that a high pith content in the finished product results in a lower grade pulp, while removable of substantially all of the pith will allow the production of newsprint grade pulp. While the use of depithed bagasse will result in a higher grade end product and will require a shorter processing time and a reduced amount of chemicals, for a lower grade pulp it may be more desirable to use the whole bagasse to avoid the additional depithing step prior to the pulping process.

When the bagasse enters the receiving chamber 24, it is in the form of pieces which consist of large bundles of fiber locked together by pith, lignin and other substances which must be removed from the finished pulp because of their detrimental effect on the properties of the products produced therefrom. Saturated steam is introduced into the receiving chamber 24 and impregnating chamber 30 through the steam pipe 26 to maintain a pressure of about 150 p.s.i.g. and the corresponding temperature of 366 F. This has been found to be the optimum temperature for maintaining sufiicient speed of pulping action while preventing excessive degradation of the cellulose. As the bagasse moves through the impregnating chamber 30, the bagasse particles are thoroughly impregnated by the chemicals added through the pipe 27 and a complete mixing takes place. By the time the bagasse reaches the outlet 34, the softening of the fiber bundles has reached the point where mechanical action can be used to separate the fibers without causing excessive breakage and degradation that would occur if the mechanical defibering action were done prior to the softening and impregnation.

The bagasse particles then enter the disc defibrator 36 where the bundles are mechanically broken apart and the fibers separated to increase the area upon which the chemicals may act during the final stages of pulping in the digesting chamber 40. The mechanical action of the disc defibrator 36 is improved by the fact that this action takes place at the full temperature and pressure of the saturated steam within the impregnating chamber 30. As the bagasse leaves the defibrator 36 through the outlet pipe 37 to enter the digesting chamber 40, flow of the bagasse is maintained by having a pressure drop of approximately psi. so that within the digesting chamber 40, the saturated steam is at a pressure of 135 p.s.i.g. and the corresponding temperature of about 358 F.

As the defibered bagasse pass through the cooking and digesting chamber 40, the screw conveyor 43 maintains a mixing action as the bagasse is conveyed toward the outlet 46 to complete the pulping process which now proceeds at a rapid rate since after the defibration the fibers have a much greater area exposed for chemical action. When the fibers reach the outlet 46, they pass into the disc refiner 48 to allow further refining and homogenization of the fiber size by the abrading action of the discs. A pressure drop takes place within the disc refiner 48 so that when the fibers are discharged into the outlet 50 as finished pulp, the pressure and temperature is much lower than that within the digesting chamber 40 and there is no need to provide a blow tank to receive the fiber. To further avoid possible flash as the pulp is discharged, water is added through the water pipe 52 to reduce the temperature of the pulp so that it may be discharged into the atmosphere for further processing action.

Depending upon the quality of the bagasse used in the process, and the chemicals employed in the pulping action, the quality of the finished pulp may be varied from what is known in the art as semi-chemical pulp to standard quality sulphite, soda, soda-sulphite and sulphate pulps. The amount of chemical consumption in the pulping process is reduced from that normally required by about 40%, and for example where the chemical equivalent would be 500 pounds per ton of finished pulp with the usual prior art process, pulp of similar quality may be produced in this process using a chemical requirement of only 300 pounds. This process requires a total treatment time of approximately 30 minutes in both the impregnating and digesting chambers, and while this time is relatively long, the length of the chambers may be such as to maintain a high rate of output in spite of the treatment time,

In producing a purified pulp from bagasse similar to standard grades of unbleached sulphite and soda pulps, a yield from whole bagasse of 50% is obtained and the yield from clean bagasse fiber will reach 65%. This pulp may be blended with an equal amount of groundwood pulp to produce a highly satisfactory sheet of paper of newsprint grade. Using the semi-chemical pulp process, a yield from whole bagasse will be approximately 60% and from clean bagasse approximately and the resulting pulp will produce a satisfactory sheet of paper suitable tor use in the manufacture of corrugated board and containers.

It is pointed out that this process is not limited to the use of sugar cane bagasse as the fiber source, but has been discussed with respect to bagasse because of the difficulties of the prior art in producing suitable grades of pulp from bagasse. It is understood that this process is adaptable to the production of pulp and fiber from other materials such as wood, wood waste, linters and the like. Further modifications and rearrangements of this invention will readily become apparent to those skilled in the art and may be resorted to without departing from the scope of the invention as set forth in the following claims.

What is claimed is:

1. The process of producing pulp from cellulosic fibrous material comprising forcing the fibrous material into a first chamber, introducing into said first chamber pulping chemicals and steam to maintain therein a first pressure substantially higher than atmospheric pressure and the corresponding temperature of saturated steam, agitating the material in said first chamber to heat the material substantially to said saturated steam temperature, discharging the material directly from said first chamber into a second chamber, mechanically defibering the material in said second chamber at substantially the pressure and temperature in said first chamber, discharging the material directly from said second chamber into a third chamber, maintaining in said third chamber a second pressure substantially higher than atmospheric pressure but lower than said first pressure, subjecting the material to the pressure drop from said first pressure to said second pressure while moving it into said third chamber, agitating the material in said third chamber at said second pressure and at the corresponding saturated steam temperature, discharging the material from said third chamber directly into a fourth chamber, mechanically defibering the material in said fourth chamber and delivering it into an outlet conduit while subjecting the material in said fourth chamber to a pressure drop from said second pressure.

2. The process claimed in claim 1 with the added step of cooling the material in said outlet conduit sutficiently to prevent flashing when the material is discharged to atmospheric pressure.

3. The process of claim 1 in which said fibrous material is depithed bagasse 5 4. The process of claim 1 in which said first pressure 2,862,813 is about 150 p.s.i.g. 2,913,362 5. The process of claim 4 in which said second pressure 2,944 929 is about 135 p.s.i.g. 2:963:05

References Cited by the Examiner UNITED STATES PATENTS 1,850,832 3/1932 Ellis 16268 1,982,130 11/1934 Wollenberg 162-17 2,200,034 5/1940 Merrill 16217 10 6 Birdseye 162-18 Cusi 162--96 Knapp et a1. 162-96 Green 162-17 DONALL H, SYLVESTER, Primary Examiner.

MORRIS O. WOLK, Examiner.

S. L. BASHORE, Assistant Examiner. 

1. THE PROCESS OF PRODUCING PULP FROM CELLULOSIC FIBROUS MATERIAL COMPRISING FORCING THE FIBROUS MATERIAL INTO A FIRST CHAMBER, INTRODUCING INTO SAID FIRST CHAMBER PULPING CHEMICALS AND STEAM TO MAINTAIN THEREIN A FIRST PRESSURE SUBSTANTIALLY HIGHER THAN ATMOSPHERIC PRESSURE AND THE CORRESPONDING TEMPERATURE OF SATURATED STEAM, AGITATING THE MATERIAL IN SAID FIRST CHAMBER TO HEAT THE MATERIAL SUBSTANTIALLY TO SAID SATURATED STEAM TEMPERATURE, DISCHARGING THE MATERIAL DIRECTLY FROM SAID FIRST CHAMBER INTO A SECOND CHAMBER, MECHANICALLY DEFIBERING THE MATERIAL IN SAID SECOND CHAMBER AT SUBSTANTIALLY THE PRESSURE AND TEMPERATURE IN SAID FIRST CHAMBER, DISCHARGING THE MATERIAL DIRECTLY FROM SAID SECOND CHAMBER INTO A THIRD CHAMBER, MAINTAINING IN SAID THIRD CHAMBER A SECOND PRESSURE SUBSTANTAILLY HIGHER THAN ATMOSPHERIC PRESSURE BUT LOWER THAN SAID FIRST PRESSURE, SUBJECTING THE MATERIAL TO THE PRESSURE DROP FROM SAID FIRST PRESSURE TO SAID SECOND PRESSURE WHILE MOVING IT INTO SAID THIRD CHAMBER, AGITATING THE MATERIAL IN SAID THIRD CHAMBER AT SAID SECOND PRESSURE AND AT THE CORRESPONDING SATURATED STEAM TEMPERATURE, DISCHARGING THE MATERIAL FROM SAID THIRD CHAMBER DIRECTLY INTO A FOURTH CHAMBER, MECHANICALLY DEFIBERING THE MATERIAL IN SAID FOURTH CHAMBER DELIVERING IT INTO AN OUTLET CONDUIT WHILE SUBJECTING THE MATERIAL IN SAID FOURTH CHAMBER TO A PRESSURE DROP FROM SAID SECOND PRESSURE. 